A 1930s film shows a dog running and jumping inside a fenced enclosure (1)—except that the dog has a strange-shaped head, odd stripes, and a rigid tail that can only move side-to-side. The “dog” is actually one of the last thylacines, a marsupial predator also called the Tasmanian tiger. The film was taken shortly before humans extinguished the species forever. Or did we? Recently, new technologies have made it plausible to try to revive many recently extinct species. Scientists around the world are discussing, and working toward, “de-extinction” (2).